1. Field of the Invention
The present invention relates to a mobile communication method, a mobile communication system, and a radio base station, in which a high speed uplink packet communication and a high speed downlink packet communication are performed between the radio base station and a mobile station.
2. Description of the Related Art
In a mobile communication system as shown in FIG. 1, an enhanced uplink (EUL)/a high speed uplink packet access (HSUPA) defined by the 3GPP is adopted as a high speed uplink packet communication, while a high speed downlink packet access (HSDPA) defined by the 3GPP is adopted as a high speed downlink packet communication.
In such a mobile communication system, an E-DCH absolute grant channel (E-AGCH), an E-DCH relative grant channel (E-RGCH), and an E-DCH hybrid ARQ indicator channel (E-HICH) are established as downlink channels (EUL control channels) from a radio base station NodeB to a mobile station UE.
In addition, in the mobile communication system, a high speed physical downlink shared channel (HS-PDSCH) and a shared control channel for HS-DSCH (HS-SCCH) are established as downlink channels (HS channels) from the radio base station NodeB to the mobile station UE.
Furthermore, in this mobile communication system, a dedicated physical channel (DPCH), a common pilot channel (PCPICH), and a common control physical channel (PCCPCH) are established as downlink channels (non-HS channels) from the radio base station Node B to the mobile station UE.
With reference to FIG. 2, description will be given for an example of a method that determines a transmission power for the HS-PDSCH, in the mobile communication system applying the HSDPA.
Firstly, a MAC-hs functional unit of a radio base station NodeB calculates a power variation margin Pmargin in each sub-frame (TTI: Transmission Time Interval), by use of the following equation 2:Pmargin=(α−1)×(PnonHS−PPCPICH−PPCCPCH)  (Equation 1),where αis a margin coefficient for a dedicated channel, PnonHS is a measured value of a total transmission power in the non-HS channel, PPCPICH is a measured value of a transmission power in the PCPICH, and PPCCPCH is a measured value of a transmission power in the PCCPCH.
Secondly, the MAC-hs functional unit of the radio base station NodeB calculates the transmission power PHSPDSCH in the HS-PDSCH in each sub-frame (TTI), by use of the following equation 2:PHSPDSCH=Ptotal−PnonHS−Pmargin−NHSSCCH×PHSSCCH  (Equation 2),where Ptotal is an upper limit of the transmission power that can be assigned to a downlink channel, NHSSCCH is the number of the set HS-SCCHs, PHSSCCH is the transmission power in each HS-SCCH.
On the other hand, in a mobile communication system in which both EUL and HSDPA are applied, EUL control channels (specifically, E-AGCH, E-RGCH, and E-HICH) are additionally established as downlink channels, in addition to the channels shown in FIG. 2.
These EUL control channels do not always transmit information. Instead, the information is transmitted when receiving an instruction from a MAC-e functional unit (EUL functional unit) of the radio base station NodeB.
Here, two possible methods will be shown as the methods for determining, at the MAC-hs functional unit of the radio base station NodeB, the transmission power PHSPDSCH in the HS-PDSCH, in consideration of the transmission power in the EUL control channels.
A first method is that the MAC-hs functional unit determines the transmission power PHSPDSCH in the HS-PDSCH in each sub-frame (TTI) always after surely reserving the transmission power required for transmitting the information through the EUL control channels.
Specifically, the MAC-hs functional unit calculates the transmission power PHSPDSCH in the HS-PDSCH in each sub-frame (TTI), by use of the following equation 3:PHSPDSCH=Ptotal−PnonHS−Pmargin−NHSSCCH×PHSSCCH−PE-AGCH (fixed)−PE-RGCH (fixed)−PE-HICH (fixed)  (Equation 3),where PE-AGCH (fixed) is the transmission power (fixed value) required for transmitting the information through the E-AGCH, PE-RGCH (fixed) is the transmission power (fixed value) required for transmitting the information through the E-RGCH, and PE-HICH (fixed) is the transmission power (fixed value) required for transmitting the information through the E-HICH.
However, in this method, the transmission power for transmitting the information through the EUL control channels is always reserved even though the information is not always transmitted on the EUL control channels. This reserved radio resources are wasted, thereby causes a problem of reducing the transmission power that can be assigned to the HS-PDSCH as the transmission power PHSPDSCH.
Meanwhile, a second method is that the MAC-hs functional unit measures the transmission power in the EUL control channels, and thereafter determines the transmission power PHSPDSCH in the HS-PDSCH in each sub-frame (TTI).
Specifically, the MAChs functional unit calculates the transmission power PHSPDSCH in the HS-PDSCH in each sub-frame (TTI), by use of the following equation 4:PHSPDSCH=Ptotal−PnonHS−Pmargin−NHSSCH×PHSSCCH  (Equation 4),where PnonHS includes measured values of the transmission power in the E-AGCH, the E-RGCH, and the E-HICH.
However, in this method, the measurement results may largely differ from the transmission power actually used (actual transmission power), due to a delay in reflecting the measurement results and an averaging of measured times for the transmission power in the EUL control channels. Accordingly, Pmargin has to be set large to some extent, and this also causes a problem of reducing the transmission power that can be assigned to the HS-PDSCH as transmission power PHSPDSCH.
In particular, since the E-AGCH requires a large transmission power, it is difficult to adjust the measurement results for the transmission power in the E-AGCH, to the actual transmission power, in accordance with the change in the number of the set E-AGCHs, that is changed from moment to moment.